Electrical contacts, such a military-style “screw machined” contacts, are typically gold plated. In order to save gold, so-call “selective plating” methods may be used in which a whole contact is plated with a very thin layer of gold in conventional plating drums, and then selective plating (e.g., adding gold as-needed) is used in specific portions of the contact such as a tip of a small contact or an interior of a female contact. A thicker layer of gold may be needed on portions of the contact where the most stressful contact between mating parts exists. It is currently a known production challenge to limit the application of gold plating (original or subsequent) to the interior of a female electrical contact.
With regard to female electrical contacts, it may be particularly desirable to apply additional plating material only the interior surface in order to minimize waste of expensive plating material such as gold, platinum and the like. Numerous prior expedients have been proposed to facilitate selective plating of articles, including those expedients described in U.S. Pat. Nos. 4,077,852, 4,280,882, 4,853,099,5,372,700, 4,555,321, 7,842,170, 4,473,445 and European Patent Application No. EP0070694.
Many of the prior expedients rely primarily on such techniques as injecting plating solution into the socket and sucking it back out, using chromate films for masking purposes, using Teflon enclosures around the electrical contact in order to create a negative capillarity which prevents wetting of the exterior of the contact with plating solution, or using cells with a matching contour for masking the exterior surface of the contact. Each of these prior expedients is deficient in one or more aspects, such as their reliability, efficiency or results.
What is needed is an improved system and method for selectively plating the interior surface of an elongated articles (such as female electrical contacts or “sockets”) in a manner which results in uniform plating, minimizes access of the plating solution to the exterior of the articles, and is more cost-effective than the prior expedients.